U.S. patent application number 10/562228 was filed with the patent office on 2007-01-11 for waste gas cleaning system for an internal combustion engine.
This patent application is currently assigned to DAIMLERCHRYSLER AG. Invention is credited to Frank Duvinage, Berthold Keppeler, Leopold Mikulic, Arno Nolte.
Application Number | 20070009398 10/562228 |
Document ID | / |
Family ID | 33520992 |
Filed Date | 2007-01-11 |
United States Patent
Application |
20070009398 |
Kind Code |
A1 |
Duvinage; Frank ; et
al. |
January 11, 2007 |
Waste gas cleaning system for an internal combustion engine
Abstract
The invention concerns an exhaust gas cleaning system for an
internal combustion engine with at least one catalytically active
component which is configured such that its catalytically active
coating comprises at least a first region with high light-off
temperature and a high temperature resistance and at least a second
region with a low light-off temperature and a reduced temperature
resistance (relative to the first region). The exhaust-gas-side
surface of the catalytically active coating in the intake region of
the catalytically active component has at least a partial diffusion
layer, or is at least partially covered by a diffusion layer.
Inventors: |
Duvinage; Frank; (Kirchheim,
DE) ; Keppeler; Berthold; (Owen, DE) ;
Mikulic; Leopold; (Weinstadt, DE) ; Nolte; Arno;
(Stuttgart, DE) |
Correspondence
Address: |
CROWELL & MORING LLP;INTELLECTUAL PROPERTY GROUP
P.O. BOX 14300
WASHINGTON
DC
20044-4300
US
|
Assignee: |
DAIMLERCHRYSLER AG
Stuttgart
DE
|
Family ID: |
33520992 |
Appl. No.: |
10/562228 |
Filed: |
June 16, 2004 |
PCT Filed: |
June 16, 2004 |
PCT NO: |
PCT/EP04/06468 |
371 Date: |
June 20, 2006 |
Current U.S.
Class: |
422/168 ;
422/171 |
Current CPC
Class: |
B01D 53/94 20130101;
F01N 3/0842 20130101; F01N 3/0807 20130101 |
Class at
Publication: |
422/168 ;
422/171 |
International
Class: |
B01D 53/34 20060101
B01D053/34 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 26, 2003 |
DE |
103 28 678.0 |
Claims
1. An exhaust gas cleaning system for an internal combustion engine
with at least one catalytically active component, wherein a
catalytically active coating of the catalytically active component
comprises: at least a first region with a high light-off
temperature and a high temperature resistance; and at least a
second region with a low light-off temperature and a reduced
temperature resistance relative to the first region; wherein, the
exhaust-gas-side surface of the catalytically active coating in an
intake region of the at least one catalytically active component
has at least a partial diffusion layer or is at least partially
covered by a diffusion layer.
2. The apparatus according to claim 1, wherein the first region,
has a lower specific noble metal content and/or a larger noble
metal particle diameter than the second region.
3. The apparatus according to claim 2, wherein: cell density in the
intake region of the catalytically active component is lower than
in a discharge region of the catalytically active component.
4. The apparatus according to claim 3, wherein: the intake region
of the catalytically active component is configured with a support
material with a high specific heat capacity; and in its discharge
region, the catalytically active component has a support material
with low specific heat capacity.
5. The apparatus according to claim 4, wherein: the catalytically
active component has a cone shape.
6. The apparatus according to claim 5, wherein: the catalytically
active coating is multiple layered; individual layers have a
differing composition; the first region is oriented toward an
exhaust-gas side; and the second region is applied on a side away
from the exhaust gas.
7. The apparatus according to claim 6, wherein: the catalytically
active coating is applied in the form of a gradient; predominantly
the region with high light-off temperature is applied in the intake
region of the catalytically active component; and predominantly the
second region is applied in the discharge region of the
catalytically active component.
8. The apparatus according to claim 5, wherein: the catalytically
active coating has at least predominantly the second region.
Description
BACKGROUND AND SUMMARY OF THE INVENTION
[0001] The invention concerns an exhaust gas catalyst system for an
internal combustion engine, with at least one catalytically active
component.
[0002] Catalytic converters ordinarily have a relatively restricted
optimal thermal functioning range for ensuring proper cleaning of
exhaust gas. In the case of NOx storage catalytic converters, for
example, the optical range is between 190.degree. C. and
500.degree. C. Below this range, they are not yet sufficiently
catalytically active to be fully functional and to store the
undesired pollutants contained in the exhaust gas and/or convert
them into harmless substances; while above this range, a very
strong deactivation is associated with a strong thermal aging,
which results ultimately in the destruction of the catalytic
converter due to overheating. Since the temperature of the
catalytic converter is determined essentially by the temperature of
the exhaust gases flowing through it, control, (in particular
limiting) of the exhaust gas temperature through mechanical means
and/or targeted cooling of exhaust gas is therefore of special
importance for the proper operation of exhaust gas catalytic
converters. No less important, however, is also the thermic
behavior of the exhaust gas catalytic converters themselves; that
is: good temperature resistance in ranges of relatively high
exhaust gas temperatures or good light-off performance in order to
be able to quickly reach their full catalytic activity so that
efficient cleaning of exhaust gas is ensured.
[0003] A method for the treatment of exhaust gases of a diesel
engine for the reduction of particle emissions is disclosed in
German patent document DE 197 18 727 C2, in which the diesel
exhaust gas is directed through two diesel catalytic converters
arranged one behind the other, with the cell density of the
downstream, second catalytic converter being greater than that of
the first catalytic converter.
[0004] One object of the present invention is to provide an exhaust
gas cleaning system for an internal combustion engine, especially
for a diesel engine, in which reaction heat conversion is
distributed uniformly over the entire length of the catalytically
active components and aging behavior is improved.
[0005] This and other objects and advantages are achieved by the
exhaust gas cleaning system according to the invention, in which
the exhaust-gas-side surface of the catalytically active coating in
the intake region of the catalytically active components has at
least a partial diffusion layer, or is at least partially covered
by a diffusion layer.
[0006] In a refinement of the exhaust gas cleaning system according
to the invention, the at least one region with high light-off
temperature and a high temperature resistance (in contrast to the
at least one other region with a low light-off temperature a
reduced temperature resistance in comparison to the former) has a
lower specific noble metal content and/or a larger noble metal
particle diameter.
[0007] In another advantageous embodiment, the cell density in the
intake region (higher and/or intermediate temperature region) of
the catalytically active component is lower than in the discharge
region (lower temperature region) of the catalytically active
component.
[0008] According, another feature of the invention, the
catalytically active component is configured in its intake region
with a support material that has a higher specific heat capacity,
and in its discharge region with a support material with a lower
specific heat capacity. As a result, a deactivation of the
catalytic converter induced by a hot spot can be suppressed in a
most advantageous manner, while at the same time good light-off
behavior can be achieved. For example, ceramic or
ceramic-containing materials and/or metals or metal-containing
materials as well as other materials suited to the particular
application purpose can advantageously be used as supporting
materials with differing specific heat capacity.
[0009] In an alternative refinement of the invention according, the
catalytically active component has a cone shape.
[0010] Furthermore, in another embodiment of the invention, the
catalytically active coating is in multiple layers, with the
individual layers having differing composition. The at least one
region with high light-off temperature in combination with a high
temperature resistance is oriented toward the exhaust gas side, and
the at least one additional region with a low light-off temperature
in combination with reduced temperature resistance in comparison
with the at least one region, is applied to the side oriented away
from the exhaust gas. The start-up temperature of a catalytically
active component is referred to as light-off temperature.
[0011] In a preferred embodiment of the invention, the
catalytically active coating with at least one region of high
light-off temperature and with at least one further region with a
low light-off temperature is applied in the form of a gradient,
with the high light-off temperature being applied predominantly in
the intake region of the catalytically active component and
predominantly the at least one other region, with a lower light-off
temperature being applied in the discharge region of the
catalytically active component.
[0012] In a further preferred embodiment, the catalytically active
coating includes predominantly or entirely the at least one further
region with a low light-off temperature in combination with reduced
temperature resistance.
[0013] The catalytically active component can, for example, be
configured as an oxidation catalytic converter, an NO.sub.x storage
catalytic converter, an SCR catalytic converter and/or as a
particle filter.
[0014] Further advantages of the invention will become evident from
the description and from the drawing. Exemplary embodiments of the
invention are illustrated in a simplified form in the drawing and
will be explained in more detail in the following description. In
the drawing:
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] FIG. 1 is a schematic depiction of a first embodiment of the
invention
[0016] FIG. 2 is a schematic depiction of a second embodiment of
the invention
[0017] FIG. 3 is a schematic depiction of a third embodiment of the
invention
[0018] FIG. 4 shows the conversion behavior of an NO.sub.x storage
catalytic converter according to the state of the art
[0019] FIG. 5 shows an optimized conversion behavior of an NO.sub.x
storage catalytic converter according to the invention.
DETAILED DESCRIPTION OF THE DRAWINGS
[0020] The schematic depiction of FIG. 1 shows an arrangement of a
catalytically active coating 1 using the example of an NO.sub.x
storage catalytic converter. Exhaust gas catalytic converters
ordinarily comprise a support material or a support body 6 with
catalytically active coating 1 applied thereto. The latter, for
example, can be applied to the support body by means of a porous
washcoat of Al.sub.2O.sub.3, SiO.sub.2, TiO.sub.2, ZrO.sub.2,
zeolites and/or mixtures thereof together with activity enhancing
additives or promoters. Frequently serving as support body for
catalytic converters are ceramic catalytic converters with a
honeycomb-like structures, preferably of cordierite or other
suitable materials. Alternatively, however, support bodies of metal
can also be used. Furthermore, the catalytically active component
can be configured in its intake region with a support material with
higher specific heat capacity and with a support material with
lower specific heat capacity in its discharge region so that
materials such as, for example, metal or metal-containing materials
and ceramic or ceramic-containing material can be jointly utilized
as support material or support body for a catalytic component.
[0021] As depicted in FIG. 1, the catalytically active coating 1 of
the NO.sub.x storage catalytic converter is constructed of
individual layers of differing composition. The at least one region
with a high light-off temperature and a high temperature resistance
2 is directed toward the exhaust side, and the at least one other
region with a low light-off temperature and a reduced temperature
resistance 3 (compared with the at least one region being applied
to the side directed away from the exhaust gas). Region 2 thus is
characterized in comparison with region 3 by a poorer
low-temperature activity, but a higher high-temperature resistance,
while region 3 in contrast has an opposite behavior and is
responsible for good overall conversion and good cold-start
behavior. Through the incorporation of region 2 in the intake
region of the catalytically active component, the activity in the
lower and/or intermediate temperature range is reduced.
[0022] Regions 2 and 3 contain platinum-group metals, in particular
platinum and/or rhodium, as catalytic converter material, as well
as alkali or earth alkali metals, which are characterized by their
storage capacity for oxides of nitrogen. This property is utilized
in NO.sub.x storage or adsorber catalytic converters. Under lean
operating conditions (.lamda.>1), the nitric oxides are
converted as follows: 2NO+O.sub.2.fwdarw.2NO.sub.2 (Pt catalytic
converter)
4NO.sub.2+O.sub.2+2BaCO.sub.3.fwdarw.2Ba(NO.sub.3).sub.2+2CO.sub.2
[0023] Under rich exhaust gas conditions (.lamda.<1), nitrogen
dioxide is desorbed back out of the storage and is converted
directly with the carbon monoxide present in the exhaust gas, into
nitric oxide:
2Ba(NO.sub.3).sub.2+2CO.sub.2).fwdarw.4NO.sub.2+O.sub.2+2BaCO.sub.3
2NO.sub.2+4CO.fwdarw.4CO.sub.2+N.sub.2 (Pt, Rh catalyzed)
[0024] The switch-over times between lean and rich operation of the
engine depend on the quantity of storage material used, the
NO.sub.x emissions and the parameters typical for all catalyzed
reactions such as gas throughput and temperature.
[0025] Furthermore, regions 2 and/or 3 can include oxygen storage
components such as a cerium compound, with the most important
substance being the cerium oxide. Oxygen storage components
equalize the air ratio fluctuations in .lamda.-1 regulated engines
since they can change their oxidation state from +III to +IV and
vice versa:
2CeO.sub.2+CO.fwdarw.Ce.sub.2O.sub.3+CO.sub.2.fwdarw.(.lamda.<1)
2Ce.sub.2O.sub.3+O.sub.2.fwdarw.4CeO.sub.2.fwdarw.(.lamda.>1) In
this manner, a constant air ratio is obtained. In addition, cerium
supports the noble metal dispersion.
[0026] In order to control the temperature resistance of catalytic
converter coatings, compounds of the elements La, Zr, etc.,
preferably as oxides, can also be contained.
[0027] The choice of the composition of regions 2, 3, in particular
the concentration of noble metal in combination with the noble
metal diameter, is closely bound with the particular exhaust gas
temperature window to which respective regions 2, 3 are exposed. As
a result, the catalytic activity of the regions can be controlled
along with other measures. Through a lower concentration of noble
metal and/or a larger particle size it is possible first to avoid
excessively large conversion immediately after intake into the
catalytic converter. As a result, excessively high temperature and
loads on the intake side of the catalytic converter can be avoided.
Second, it can be provided through the selection of a relatively
large concentration of noble metal and of a relatively small
particle size that in the downstream region the required activity
for conversion of the pollutants is present in sufficient degree,
or can even be increased.
[0028] Furthermore, the exhaust-gas-side surface of catalytically
active coating 1 in the intake region of the NOx storage catalytic
converter at least partially has a diffusion layer 4 or is at least
partially covered by a diffusion layer 4. The diffusion layer
itself essentially contains oxides of aluminum, cerium and/or
zirconium and causes a kinetic retardation of the chemical
reactions proceeding at this location, in particular transport or
diffusion processes. In this manner, temperature peaks (so-called
hot spots) are advantageously suppressed in the catalytic converter
intake region, and the thermal load in the intake region is
reduced, without impairing the cold start behavior of the
system.
[0029] The manufacture of catalytic converters is well documented
in the literature in terms of the general procedure.
[0030] By variation of the cell densities (in the intake region of
the catalytic converter lower cell densities, for example 200 to
400 cpsi, and in the discharge region of the catalytic converter
higher cell densities, for example 600 to 900 cpsi) and the use of
conical catalytic converter structures (a narrower catalytic
converter diameter in the intake region and an increasing diameter
in the discharge region), the sojourn time for the exhaust gas in
the different catalytic converter regions can be controlled. That
is, in the intake area high flow speeds prevail while in the back
region, a longer sojourn time of the exhaust gas and thus a greater
conversion plays a role.
[0031] FIG. 2 is a schematic representation of an example of a
variant according to the invention of a catalytically active
coating 1 using the example of a NO.sub.x storage catalytic
converter. (For the sake of simplicity, the same reference
characters are used for the same components or components achieving
the same function and to this extent reference can be made to the
above description for FIG. 1.) In other respects, the advantages
mentioned in FIG. 1 and in the general part of the description
likewise apply for the embodiment according to the invention in
FIG. 2 and for all subsequently mentioned embodiment forms.
[0032] The exhaust gas aftertreatment apparatus of FIG. 2 includes
a catalytically active coating 1 with at least one region with high
light-off temperature and a high temperature resistance 2, and with
at least one other region with a low light-off temperature and a
reduced temperature resistance 3 in comparison with the at least
one region. The region 5, comprising the regions 2 and/or 3, is
applied in the manner of a gradient to the catalytic converter
support: Within the intake area E of the catalytic converter
predominantly the region with high light-off temperature 2 is
applied, and in the discharge area A of the catalytic converter
predominantly the at least one other region with a low light-off
temperature 3 is applied. The exhaust-gas-side surface of the
catalytically active coating 1 in the intake region of the NO.sub.x
storage catalytic converter likewise has at least partially a
diffusion layer 4, or is at least partially covered by a diffusion
layer 4.
[0033] FIG. 3 is a schematic representation of an example of a
further variant according to the invention, of a catalytically
active coating 1 using the example of an NO.sub.x storage catalytic
converter, in the case of which region 3 is provided on the
catalytic converter support. The exhaust-gas-side surface of the
catalytically active coating 1 in the intake region of the NO.sub.x
storage catalytic converter in like manner also has at least one
diffusion layer 4, or is at least partially covered by a diffusion
layer 4.
[0034] In FIG. 4, the total conversion of a conventional NO.sub.x
storage catalytic converter is plotted as a function of the
catalytic converter length. The steep rise of the curve at the
beginning clearly shows the high activity of the catalytic
converter and the associated high exothermy of the reaction in its
intake region. This leads to premature aging or even damage in the
intake region of the catalytic converter.
[0035] FIG. 5 in contrast demonstrates an optimized conversion
behavior, which is retained with all embodiment forms according to
the invention. It is possible to utilize the recommended measures
for optimization of conversion individually or in combination.
Through the invention, the conversion (and above all the associated
exothermy, i.e. the quantities of heat released in the catalytic
reaction) advantageously are distributed more uniformly on the
entire NO.sub.x storage catalytic converter. The thermic load of
the first region of the catalytic converter region is thereby
reduced, without impairing the cold-start behavior of the system.
In addition, temperature peaks in the intake region are thus
effectively avoided.
[0036] The foregoing disclosure has been set forth merely to
illustrate the invention and is not intended to be limiting. Since
modifications of the disclosed embodiments incorporating the spirit
and substance of the invention may occur to persons skilled in the
art, the invention should be construed to include everything within
the scope of the appended claims and equivalents thereof.
* * * * *